I have a similar situation with my '91.

It only happens if I turn the engine on too quickly.   If I turn the
ignition key all the way without starting the engine, and wait 3 seconds
before starting, the light never flashes.

If I don't wait that 3 seconds, the light usually flashes for a random
period of time.

maybe it's just starting to develop character.

Dave.
'91 westy GL
Napa, CA

>Hi all!  My 86 Vanagon, Stella, has recently regained consciousness (her
>transmission was rebuilt).  Anyway, I've noticed that the warning light
>for the coolant has been staying on after I start her up.  The problem
>usually resolves itself after I turn her off, and restart.  I have
>checked the coolant levels, and all is fine.  I had the sensor replaced
>in March or so.  Any suggestions on why this crazy little light is
>pestering me?
>
>Peace, Love, and Granola
>Kat